Roll back carriers are very common today. Essentially they comprise a sub-frame structure, a lift frame mounted to the sub-frame and a roll back load bed mounted on the lift frame. The sub-frame structure is designed to be mounted to the chassis of a vehicle such as a truck.
In operation the lift frame can be tilted with respect to the sub-frame and the load bed can then be rolled back to where the same engages the pavement, ground or other underlying support surface supporting the vehicle. In the rolled back position, the load bed assumes a convenient posture for loading.
Roll back carriers are commonly used to transport vehicles and especially disabled vehicles from one location to another. By using a winch, a vehicle can be pulled on the inclined load bed, after which the load bed is advanced forwardly by power means operatively interconnected between the lift frame and the load bed. After this the lift frame can be lowered downwardly to a generally horizontal transport position.
It is desirable, and in fact generally required by law, that the lift frame be securely locked to the sub-frame when the lift frame and load bed are disposed in horizontal transport positions. This obviously is a safety feature and prohibits the lift frame and load bed from inadvertently being tilted during transport and the load falling from the vehicle. The requirement of a locking mechanism for locking the lift frame to the sub-frame has been the source of a real problem with respect to roll back carriers for a long time. Often these designs have required that a latching mechanism or locking assembly be manually activated and deactivated. The result of this is that often the operator inadvertently forgets to complete the locking arrangement. Even more importantly, the operator may forget to unlock the lift frame from the sub-frame prior to actuating the hydraulic lift cylinders that raise the lift frame above the sub-frame. The latter case presents a real problem because of the potential for structural damage to the locking mechanism and the roll back carrier in general.
Therefore, there is a need for an automatic self-locking mechanism for securely locking the lift frame of a roll back carrier to the sub-frame once the lift frame assumes a generally horizontal transport position.